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101.
The Dahuiyeh (Zarand) earthquake of 2005 February 22 in central Iran: reactivation of an intramountain reverse fault 总被引:3,自引:0,他引:3
102.
J.F. Dumont E. Santana F. Valdez J.P. Tihay P. Usselmann D. Iturralde E. Navarette 《Geomorphology》2006,74(1-4):100-123
The San Lorenzo area belongs to the Esmeraldas–Tumaco seismic zone where some of the strongest earthquakes of South America occurred during the 20th century. This paper provides evidence for a succession of geomorphic changes characterized by the disruption of the Quaternary drainage network and the reshaping of the Cayapas–Santiago estuary. The rise of the La Boca uplift bordered by the La Boca and San Lorenzo faults is responsible for the southward diversion of the Palabi, Tululbi, Bogotá and Carolina rivers toward the Santiago and Cayapas rivers. The increase of the discharge directed to the Cayapas River generated the change of the channel pattern downstream from the confluence, and the avulsion of a new estuary through the coastal plain. According to the dating of beach ridges the avulsion occurred in the period 3200–2800 BP. This period corresponds also to a faster accretion of the beach ridge margin, interpreted as a response to a small uplift of the shore. The coherency of the three morphologic evidences—diversion of drainage network, avulsion and increase of coastal accretion—suggest a unique morphotectonic event, in relation with the activity of the Esmaraldas–Tumaco seismic zone. The opening of a direct communication through the mangrove margin may have brought favorable conditions for the development of the La Tolita archaeological site after 3000 BP. 相似文献
103.
本研究采用SAM剪切波分裂分析方法,使用福建区域数字地震台网记录到的(1999年01月~2003年12月)的波形资料,挑选符合剪切波窗口条件的记录,得到华夏地块东南部地区23°N~29°N,116°E~120°E)10个台站的剪切波分裂参数. 研究结果表明,该区域快剪切波平均偏振方向为NW109.4°±42.6°,慢剪切波平均时间延迟为2.5±1.5(ms/km),快剪切波平均偏振方向对应该区的水平主压应力方向. 闽东台站NW方向的快剪切波偏振优势方向揭示了NW向的水平主压应力和NW走向断裂的构造意义. 两个闽西台站NE方向的快剪切波偏振优势方向与区域水平主压应力方向不一致,与NE走向的断裂一致,体现了局部构造和局部应力场的复杂性. 本研究证实,位于活动断裂上的台站的快剪切波偏振方向的优势方向与断裂走向一致,位于海边或岛上的台站的快剪切波偏振方向较为离散,主要是受到不规则表面地形和断裂交汇的影响. 慢剪切波延迟时间的空间分布特征,显示沿海地区慢剪切波延迟时间变化较大,而内陆地区则较为平缓. 相似文献
104.
Reena De S. G. Gaonkar B. V. Srirama Sagina Ram J. R. Kayal 《Journal of Earth System Science》2003,112(3):413-419
A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring
of the January 26th, 2001 Bhuj earthquake (M
w 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one
in the NE direction and the other in the NW direction. Fault-plane solutions of the best-located and selected cluster of events
that occurred along the NE trend, at a depth of 15–38 km, show reverse faulting with a large left-lateral strike-slip motion,
which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth <10 km, on the other
hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a
depth of 15–38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip
motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults
has been the source area for stress concentration to generate the main shock and the aftershocks. 相似文献
105.
In Italy, the horizontal stress directions are well constrained in many regions, but the tectonic regime is not well known because the stress magnitudes are unknown. Our intention is to improve the knowledge of crustal stress in Italy, both at shallow depth and in low seismicity areas. Therefore, we inferred the tectonic regime from the comparison between the depth of breakout occurrence and the physical properties of the rocks in 20 boreholes. The critical value of the maximum horizontal stress, for which the effective tangential stress at the borehole wall overcomes the rock strength to form breakouts, could be computed from rock strength and density. Comparing the theoretical stress distributions for different tectonic regimes with the depth distribution of breakout occurrence, it is possible to infer the tectonic regime that fits best to the breakout depth distribution. We investigated boreholes up to 6 km deep located in different tectonic environments over the Italian peninsula: the Po Plain, the Apenninic chain, the Adriatic foredeep and the Tyrrhenian Quaternary volcanic region. These wells are characterised by breakout data of good quality (A, B and C, according to World Stress Map quality ranking system). The results are in general agreement with the style of faulting derived from earthquake focal mechanisms and other stress indicators. Our results show a predominance of a normal faulting (NF) regime in the inner Apennines and both normal faulting and strike–slip faulting (SS) style in the surrounding regions, possibly also associated with changes in the tectonic regime with depth. 相似文献
106.
A detailed investigation permitted us to obtain quantitative data concerning fine geometric structures of 4 faults of the active Maxianshan-Xinglongshan fault system and the latest movement along them. Of them the northern Maxianshan border fault is a large-scale, strongly active Holocene reverse sinistral strike-slip fault, the other 3 faults, the southern Maxianshan border fault and the southern Xinglongshan border and the northern Xinglongshan border faults are the accompanying active late-Pleistocene thrust faults, which are incorporated into the main strike-slip fault, the northern Maxianshan border fault at depth. It is the most important earthquake-controlling fault in the Lanzhou area, the fault influences and constrains the seismic activity in the area. 相似文献
107.
108.
109.
由于工程需要,对广梧高速公路(马安—河口段)的地震地质情况进行了考察,马安—河口路段所处大地构造性质为东南地洼区,穿越了三个次级构造分区:白土断陷、思劳断隆、云浮断隆。路段附近发育3条断裂:肇庆断裂、河口断裂和吴川—四会断裂。前两者为非活动断裂,后者为活动断裂且星北东向从思劳附近穿过,是未来5.0级地震发生地段,烈度可达Ⅵ度。但路段附近地震活动水平较低,仅发生过4以—5.0级地震4次,最大烈度为Ⅴ度。白诸立交、河口立交的地震地质环境稳定,思劳立交基本稳定,沿线不易产生滑坡与崩塌。 相似文献
110.